A phenomenological Li-ion cell degradation model, pertaining to charge-discharge cyclic fatigue, is proposed and validated. It is known that Solid Electrolyte Inter-phase (SEI) formation on the particle surfaces consumes active Li leading to capacity loss. The problem is further aggravated by the creation of fresh surfaces by the fracture that develops as a result of intercalation induced stresses. In addition, fracture could result in isolation of chunks of electrode material or SEI could electronically isolate certain electrode material zones, both essentially rendering the active Li or electrode material ineffective. The degradation leads to increase in electronic resistance and decrease of ionic conductivity as well as diffusivity. Central to the model is a parameter expressed as the normalized reaction surface area, diminishing with charge-discharge cycles. Here, we develop phenomenological evolution expressions for the Fracture, SEI formation and Isolation, and incorporate them in Newman's Porous Composite Electrode framework. The model is implemented in the battery module of COMSOL. Notably, the utility of a lumped parameter ‘ΔSOC*SOCmean’, based on the State of Charge (SOC) is brought out.

The rapid expansion of hybrid and alternative fuel vehicles into the marketplace will make a significant impact on greenhouse gas emissions and reduction in dependence on volatile world oil market. However, there are several obstacles preventing mass adoption of these automotive improvements. These obstacles include alternative energy costs, fluctuation in oil prices, and supplies of alternative energy. This paper will analyze the Chevy Volt Extended Range Electric Vehicle (EREV) gas savings, CO2 reduction, and reduction in oil consumption based on a real world model derived from actual vehicle and driver profiles. The benefits of the Volt and other alternative energy vehicles are dependent upon the number of vehicles used by the overall population. Government regulations and the price of oil will greatly influence the rapid adoption of these vehicles. EREV vs. PHEV:The Chevy Volt is an Extended Range Electric Vehicle (EREV) which uses a 16 kWh battery pack to provide up to 40 miles all electric range in Charge Depleting (CD) mode. A small gas engine provides Charge Sustaining (CS) power when the battery has depleted its CD capacity extending the vehicle range to 300 miles. An EREV is often assumed to be a large Plug-In Hybrid Electric Vehicle (PHEV), however, there are unique differences between EREVs and PHEVs which have significant impact on the proceeding analysis.In simple terms, when comparing EREV's and PHEV's, PHEV's are similar to a Hybrid Electric Vehicle (HEV), while EREV's are more similar to an Electric Vehicle (EV). The Chevy Volt EREV is designed to operate as a fully operational electric vehicle with the added assurance of a gas tank to extend the vehicle's useful operation through the day, eliminating range anxiety experienced by electric vehicle drivers. The Volt provides full vehicle performance during the charge depletion mode, including the ability to accelerate from 0 to 60 miles per hour in 9 seconds without needing assistance from the engine. The gas engine is only used to sustain the battery state of charge (SOC) when the battery reaches a targeted point. Conversely, PHEV's provide additional battery capacity to allow operation in electric only mode, but performance is typically limited. The gas engine is required to provide full performance, such as when accelerating at full throttle while entering a highway or using high auxiliary loads. The electric range capacity is generally characterized by the mile range the vehicle can operate in electric drive, i.e., PHEV-10 represents an HEV capable of driving 10 miles in electric drive during city driving on the Urban Dynamometer Driving Cycle (UDDS) in contrast to an EREV-40 that represents a vehicle capable of driving 40 miles in electric drive during the high acceleration drive cycle (US06). Another style of PHEV is a blended style, which is typically found in conversion hybrid kits. These vehicles start and operate with the engine on and cycles the engine on and off throughout the battery depletion. The extra capacity stored in the battery ...

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A numerical study is performed on the cyclic capacity degradation of a lithium manganese oxide (LMO) cell, under 21 different combinations of temperature and state of charge (SOC), based on the phenomenological model developed earlier. Out of the 21 sets, six are used for fitting in order to establish the degradation parameters of the model and the rest could be predicted with an average accuracy of about 90%. Two optimization algorithms (Genetic and Nelder Mead) are used and the consistency of the convergence is verified. The discussion includes sensitivity analysis of a selected set of degradation parameters. In addition, an analysis of the evolution of solid electrolyte interphase (SEI) and isolation (islanding) mechanisms under varying conditions of SOC and temperatures is performed which brings out the relative contribution of each mechanism to the overall capacity fade.